More than a century after its first description through G.H. Whipple, the understanding of the chronic multisystemic infection called Whipple's disease is still limited. However, within recent years the knowledge about diagnosis and treatment, the pathogenesis, and the biology of the agent itself have been improved by molecular biological and immunological methods. Despite the ubiquitous presence of the causative bacterium Tropheryma whipplei, Whipple's disease is very rare, and immunogenetic host factors rather than the genotype of the agent influence the course of infection. Since the clinical features of classical Whipple's disease are non-specific and the spectrum of isolated organ-specific manifestations might be underestimated, diagnosis often still is a challenge. Moreover, besides classical Whipple's disease, there are newly recognized infections with T. whipplei, which do not fit in the concept of classical Whipple's disease, for example, acute self-limiting infection and isolated T. whipplei endocarditis. Antibiotic therapy is usually successful. However, several problems are still unresolved, of which the most important are the following: which antibiotic should be used; how long treatment should be continued; how the immunoreconstitution inflammatory syndrome, which may occur after initiation of treatment, should be managed; and which is the best treatment of severe neurological manifestations.